Internal combustion engines generally include a piston that is mounted for reciprocation within a cylinder. The piston is coupled to a crankshaft by a connecting rod such that the reciprocation of the piston rotates the crankshaft. One end of the connecting rod is rotatably connected to a crankpin of the crankshaft and the other end of the connecting rod is connected to a wristpin of the piston. The wristpin can be rotatably connected to the piston and rigidly connected to the connecting rod such that the connecting rod and wristpin rotate relative to the piston as the piston reciprocates within the cylinder. Alternatively, the wristpin can be rigidly connected to the piston and rotatably connected to the connecting rod so that the connecting rod rotates relative to the wristpin and the piston as the piston reciprocates within the cylinder.
A number of different methods are used to lubricate the wristpin bearing surface. Typically, a hole drilled in the connecting rod transports lubricant supplied from the crankpin to the wristpin. When the connecting rod is rotatably connected to the wristpin, the hole supplies lubricant directly to the bearing surface between the connecting rod and the wristpin. When the connecting rod is rigidly connected to the wristpin, the hole directs lubricant to a passageway through the wristpin to supply the lubricant directly to the bearing surface between the piston and the wristpin.
It is also known to introduce lubricant into internal passageways within the piston to cool the piston during operation of the engine. Typically, a collimated jet of oil from an injection nozzle is directed into the cooling passageways to remove heat from the piston. In some configurations, the lubricant exits the cooling passageways from the underside of the piston and falls toward the wristpin to assist in lubricating the wristpin bearing surfaces. For example, the top of the connecting rod can include a hole that catches the exiting lubricant and that directs the lubricant to the bearing surface between the connecting rod and the wristpin. Historically, the wristpin has been spaced a distance from the lower surface of the piston and therefore the configurations disclosed in the prior art are incapable of directly lubricating the wristpin bearing surfaces with the lubricant exiting the cooling passages.